1. Field of the Invention
The present invention relates to an illuminating apparatus for testing which is particularly suitable to examine hole-clogging in a catalyst for automobiles perforated to make through-holes and which is also used to examine conditions of the holes in the substrate perforated to make through-holes or the inner surface of a cylindrical member having through-holes.
2. Description of the Background Art
As the above-mentioned illuminating apparatus for testing, a apparatus for checking whether holes formed in the catalyst for automobiles are clogged or not will be taken up as an example. The apparatus comprises an illuminating means for emitting light on the catalyst from the direction its holes are formed; and a telecentric lens for narrowing the light which has passed through the holes after having been emitted by the illuminating means so that the light can be taken into an imaging means. The light taken into the imaging means is shown on a monitor or the like to determine the presence or absence of clogged holes.
Using the telecentric lens to measure a cubic tested target has the advantage of performing high precision image processing without causing the target to be out of focus; however, it has the disadvantage of increasing the cost of the entire apparatus because of the high price of the lens. The disadvantage becomes pronounced when a tested target to be imaged is large because it requires a large telecentric lens.
In general, a telecentric lens, which is thicker than other lenses, has the disadvantage that a larger illuminating apparatus is required in the direction of illumination.
In view of the above-described situation, the present invention has the object of providing an illuminating apparatus for testing which is cost effective and small in size.
In order to solve the above-described problems, the illuminating apparatus for testing of the present invention comprises: an illuminating means having a predetermined illumination angle; a first lens for converging light from the illuminating means and converting the light into collimated light; and a second lens for converging light which has passed through through-holes formed in a tested target after having been emitted from the first lens as the collimated light and for making an imaging means take in the light.
The light emitted with a predetermined illumination angle from the illuminating means is converted into collimated light by the first lens, and applied to the tested target. The light passed through the through-holes of the tested target is converged by the second lens to be taken into the imaging means. The light taken into the imaging means is subjected to an imaging process and shown on a monitor or the like, which can determine the presence or absence of clogging in the through-holes. It goes without saying that this apparatus can reduce cost, as compared with apparatus utilizing an illuminating means for emitting collimated light (a surface illuminant which illuminates in the form of surface (also called backlight)). In addition, utilizing the illuminating means for emitting light with an illumination angle can miniaturize the illuminating means itself. Since the tested target to be imaged does not change its position, it is meaningless to use the conventional telecentric lens, and it does not cause any problem to use a normal lens.
The illuminating apparatus for testing can comprise: an illuminating means having a predetermined illumination angle; a first total reflection mirror for changing the orientation of the optical axis of light emitted from the illuminating means to a nearly orthogonal direction; a second total reflection mirror for changing the orientation of the optical axis of light reflected by the first total reflection mirror to a nearly orthogonal direction, thereby turning the reflected light to the direction opposite to the direction the illuminating means emits light; a first lens for converging the light reflected by the second total reflection mirror and converting the light into collimated light; a second lens for converging light which has passed through through-holes formed in a tested target after having been emitted from the first lens as the collimated light; a third total reflection mirror for changing the orientation of the optical axis of light from the second lens to a nearly orthogonal direction; and a fourth total reflection mirror for changing the orientation of the optical axis of the light reflected by the third total reflection mirror to a nearly orthogonal direction, thereby making an imaging means take in the reflected light towards the same direction as the direction the illuminating means emits light.
The orientation of the light from the illuminating means is changed to the direction opposite to the direction of illumination by the first total reflection mirror and the second total reflection mirror. Utilizing the two total reflection mirrors expands the illumination angle of the light emitted from the illuminating means at two steps. The light reflected by the second total reflection mirror is converted into collimated light by the first lens and applied to the tested target. The light passed through the through-holes of the tested target is converged by the second lens, and its orientation is changed to the same direction as the direction the illuminating means emits light via the third total reflection mirror and the fourth total reflection mirror. Then the light is taken in by the imaging means. Using the two total reflection mirrors can secure the light converged by the second lens to be converged in two steps so as to be taken in the imaging means. In addition, arranging the illuminating means and the imaging means by being displaced from the direction to radiate the tested target can achieve the miniaturizing of the illuminating apparatus in the direction of illumination, as compared with the case where they are aligned in the direction of illumination.
Adopting Fresnel lenses as the first lens and the second lens can achieve further downsizing of the illuminating apparatus. Fresnel lenses, which are readily processed, could be made into a square contour or drilled.
When the tested target has a lot of fine holes such as a catalyst for automobiles, the illuminating apparatus for testing is useful.
The illuminating apparatus can be miniaturized in the direction orthogonal to the direction to emit light by arranging the illuminating means and the imaging means on the same side so that the optical axis of the illuminating means and the imaging center axis of the imaging means are substantially in a coaxial position.
Forming the second lens to be a workbench of the tested target not only makes a special workbench unnecessary but also puts the tested target as close to the imaging means as possible.